Some vehicle engines implement an ignition system where a separate ignition coil is connected to each spark plug without the use of a distributor and spark plug wires in what is commonly referred to as a coil-on-plug ignition system. The coil-on-plug ignition system provides various benefits relative to other types of ignition systems. For example, the coil-on-plug ignition system allows each ignition coil a longer time to accumulate a charge between sparks relative to an ignition system where a single ignition coil provides charge to a plurality of spark plugs. Accordingly, the coil-on-plug ignition system provides a higher energy spark relative to other such systems.
FIG. 1 shows one example of an ignition system 100 having a coil-on-plug configuration for one cylinder of an engine. The ignition system 100 includes an ignition coil 102. A camshaft cover 104 forms a passage 106 where the ignition coil 102 is inserted to gain access through the camshaft cover 104 to a spark plug (not shown). The ignition coil 102 connects to a terminal of the spark plug in order to provide an electrical charge to the spark plug.
The ignition coil 102 is bolted to the camshaft cover 104 to secure the ignition coil in the passage 106 so that the ignition coil 102 remains connected to the spark plug. In particular, the ignition coil 102 comprises a mounting arm 108 that extends away from the passage 106 and protrudes over the camshaft cover 104. The mounting arm 108 comprises a threaded portion 110 for receiving a fastener (e.g., a bolt) 112. Correspondingly, the camshaft cover comprises a threaded portion 114 to receive the fastener 112. Further, the camshaft cover 104 comprises a mounting boss 116 for aligning the mounting arm 108 with the camshaft cover 104 so that the threaded portion 110 of the mounting arm 108 aligns with the threaded portion 114 of the camshaft cover 104 so that that fastener 112 can be screwed into the threaded portion 110 and further into threaded portion 114 to secure the ignition coil 102 to the camshaft cover 104.
However, the inventors have recognized several potential issues with such a configuration. For example, by bolting the ignition coil to the camshaft cover, the tolerances of each component stack up so that variations in dimensions and tolerances of the components create additional interference or reduced clearance. This in turn results in component deflection upon assembly and/or increased wear that reduces the operational life of the components. Moreover, noise, vibration, harshness (NVH) characteristics of the camshaft cover are transferred to the ignition coil resulting in reduced connection stability and/or increased wear.
In one example, the above mentioned issues may be addressed by an ignition system comprising: a spark plug comprising a spark plug terminal; an ignition coil comprising a barbed terminal; a housing covering the spark plug, the housing forming a passage for the ignition coil to access the spark plug; and a retaining apparatus comprising: a first spring clip to retain the barbed terminal; and a second spring clip to retain the spark plug terminal to mate the ignition coil to the spark plug. In one particular example, this enables the ignition coil not to be mounted to the camshaft cover, if desired.
By mating the ignition coil to the spark plug with the retaining apparatus instead of mounting the ignition coil to the camshaft cover, for example, the stack up of tolerances of the ignition coil can be reduced. In this way, the connection between the ignition coil and the spark plug can be made more stable and consistent and the operating life of the components can be increased due to reduced wear. This configuration may be especially beneficial in engines that utilize floating composite camshaft covers that are isolated from the cylinder head by an insolating layer, because the camshaft cover has a greater tendency to change position relative to the position of the spark plug as a result of NVH.
Moreover, since the ignition coil is not mounted to the camshaft cover, various mounting features of the ignition coil and the camshaft cover can be eliminated, if desired. In particular, the mounting arm and the threaded portion can be eliminated from the ignition coil and the mounting boss and the threaded portion can be eliminated from the camshaft cover. In addition, the fastener can be eliminated from the ignition system. In this way, the ignition system can be made less complex resulting in a reduction in production costs.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.